Does Using A Microwave Really Save Energy?

Dear EarthTalk: How does the microwave compare in energy use, say, to using a gas or electric stove burner to heat water for a cup of tea? — Tempie, Dexter, MI

The short answer is that it depends upon several variables, including the price of electricity versus gas, and the relative efficiency of the appliances involved. Typically, though, a microwave would be slightly more efficient at heating water than the flame on a gas stove, and should use up a little less energy. The reason: The microwave’s heat waves are focused on the liquid (or food) inside, not on heating the air or container around it, meaning that most if not all of the energy generated is used to make your water ready.

Given this logic, it is hard to believe that a burner element on an electric stovetop would be any better, but an analysis by Home Energy Magazine found otherwise. The magazine’s researchers discovered that an electric burner uses about 25 percent less electricity than a microwave in boiling a cup of water.

That said, the difference in energy saved by using one method over another is negligible: Choosing the most efficient process might save a heavy tea drinker a dollar or so a year. “You’d save more energy over the year by replacing one light bulb with a CFL [compact fluorescent lightbulb] or turning off the air conditioner for an hour—not an hour a day, one hour at some point over the whole year,” says consumer advocate Michael Bluejay.

Although a microwave may not save much energy or money over a stove burner when heating water, it can be much more energy-efficient than a traditional full-size oven when it comes to cooking food. For starters, because their heat waves are concentrated on the food, microwaves cook and heat much faster than traditional ovens. According to the federal government’s Energy Star program, which rates appliances based on their energy-efficiency, cooking or re-heating small portions of food in the microwave can save as much as 80 percent of the energy used to cook or warm them up in the oven.

The website Treehugger.com reports that there are other things you can do to optimize your energy efficiency around the kitchen when cooking. For starters, make sure to keep the inside surfaces of your microwave oven clean so as to maximize the amount of energy reflected toward your food. On a gas stovetop, make sure the flame is fully below the cookware; likewise, on an electric stovetop, make sure the pan or kettle completely covers the heating element to minimize wasted heat. Also, use the appropriate size pan for the job at hand, as smaller pans are cheaper and more energy-efficient to heat up.

Despite these tips for cooking greener, Bluejay reiterates that most of us will hardly put a dent in our overall energy use just by choosing one appliance over another. According to his analysis, for someone who bakes three hours a week the cheapest cooking method saves only an estimated $2.06/month compared to the most expensive method.

“Focusing on cooking methods is not the way to save electricity [at home],” says Bluejay. “You should look at heating, cooling, lighting and laundry instead.”